Emulsions which contain essentially tabular silver halide grains are well known in the prior art. These grains provide some advantages over more conventional, spherical grains. For example, silver halide X-ray elements containing tabular grains can be fully forehardened and yet maintain excellent covering power. This is an advantage over conventional X-ray elements containing spherical grains which are normally hardened during the processing steps. Additionally, tabular grains can be coated at a lower coating weight and thus have a silver savings over elements containing conventional grains. Also, elements containing tabular grains sometimes exhibit a higher speed than those with spherical grains. However, since tabular grains have low sensitivity to blue light, there is a pressing need to provide satisfactory spectral sensitizing dyes therefor and thus be able to use all the advantages provided by these tabular grains. Spectral sensitizing dyes reported in the prior art used mainly for spherical grains, can also be used with tabular grain elements. However, they generally must be used at high levels when incorporated with silver halide grains and this can lead to undesirable stain, fog and processing artifacts. Stain is particularly unsatisfactory when present in X-ray elements, for example. Here, it is conventional to use a blue-tinted film support. Conventional dyes when used with tabular containing silver halide elements tend to leave a yellow or muddy brown color and this is particularly objectionable for this use.
Spectral sensitizing dyes which J-aggregate are also well known in the prior art. J-aggregation causes a single dye, or a mixture of dyes, to shift the absorption maxima to a longer wavelength. Dyes which J-aggregate are of major practical importance since they are sharp and have high absorption coefficients giving selective sensitization. Although a number of dyes have been reported as being particularly useful with tabular grains, few or none appear to possess the ability to J-aggregate thereon in the 400 to 500 nm spectral range.